Petrology, geochemistry, and Na-metasomatism of Triassic-Jurassic non-marine clastic sediments in the Newark, Hartford and Deerfield rift basins, northern United States.

van de Kamp, Peter C. and Leake, Bernard E. 1996. Petrology, geochemistry, and Na-metasomatism of Triassic-Jurassic non-marine clastic sediments in the Newark, Hartford and Deerfield rift basins, northern United States. Chemical Geology 133 (1-4) , pp. 89-124. 10.1016/S0009-2541(96)00071-X

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Abstract

Many sandstones and associated siltstones and shales of the Triassic-Jurassic Newark Supergroup in the Newark, Hartford, and Deerfield rift basins are immature feldspathic alluvial and lacustrine closed-basin deposits. They were derived from felsic igneous and metamorphic continental blocks on the flanks of their depositional basins. The provenance was dominantly calc-alkaline basement rocks similar to the Sierra Nevada of California. The physical and chemical environments of erosion and deposition were probably similar to those in moist Pleistocene-Holocene alluvial basins and playas in the Great Basin of California and Nevada. New petrographic and geochemical data for 113 samples indicate that albite-rich sandstones and shales of the Stockton, Lockatong, and Passaic Formations in the Newark Basin and in the Portland and East Berlin Formations of the Hartford Basin and analcime-rich shales (up to 52% normative analcime) of the Lockatong Formation have unusually high Na2O contents (4–7%). Textural evidence indicates both sodium replacement in feldspars and formation of authigenic albite and analcime in these rocks. By comparison with modem sediments derived from similar provenance, using mixing models, it is estimated that up to 4% Na2O was diagenetically added to the detrital clastics. Trace metals (Co, Cr, Cu, Ni, Zn) abundances were apparently enhanced by deposition from brines in the Lockatong Formation. Analcime deposition occurred in shales with ; this ratio is found only in sediments to which Na has been added from salts/brines. Source rocks and the weathering products derived from them may be considered as a closed system in which sodium was retained partly in solids, as feldspar, and part went into solution during weathering. The dilute solution migrated into the depositional basin where evaporation yielded concentrated brine during semi-arid to arid climate in the drier parts of ∼ 21,000-yr Milankovitch cycles. Reaction of brine during diagenesis at near surface and/or shallow depths (< 2 km) with Ca-plagioclase, K-feldspar, and layer silicates at estimated temperatures < 50°C to ∼ 100°C and pH 7–9 + yielded thermodynamically stable authigenic albite and analcime in the sodium-metasomatised clastic sediments. Low activity of K+ precluded development of authigenic K-feldspar. However, K+ from solution incorporated into muds and silts as smectites were transformed to illite. Some Lockatong beds contain anomalously high P2O5, Ce, La, Y, Th, and U in authigenic apatite or monazite, suggestive of mobilization of these elements in diagenesis.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Publisher:	Elsevier
ISSN:	0009-2541
Date of Acceptance:	30 April 1996
Last Modified:	09 Jul 2020 15:00
URI:	https://orca.cardiff.ac.uk/id/eprint/133066

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